Rheumatoid arthritis (hereinafter referred to as RA) is a chronic disease that inflames joints and nearby areas. Besides the joints, other tissues can also be affected by RA. Patients with RA usually have overreactive T cells. Therefore, RA can be categorized as an autoimmune disease.
Leflunomide, N-(4-trifluoromethylphenyl)-4-carboxamidyl-5-methylisoxazole, is a drug for treating RA introduced into the market in recent years. Leflunomide and its main metabolite, malononitrilamide (MNA), were first made by Hoechst Marion Roussel. 
The objectives of this invention are as follows:
1. To synthesize a series of novel analogs of leflunomide,
2. To conduct in-vivo studies to evaluate the efficacy of the analogs, and
3. To select the leflunomide analogs that can be used for treating rheumatoid arthritis.
This invention comprises the syntheses of a series of novel analogs of leflunomide for treating Rheumatoid Arthritis. To the best of our knowledge, these analogs have not been disclosed by any other parties. The in-vivo animal studies indicate that these leflunomide analogs are surpassingly more effective than leflunomide.
Representative syntheses and in-vivo animal studies are described as follows:

Wherein DCC is N,Nxe2x80x2-dicyclohexylcarbodiimide and TEA is triethylamine.
Method 1:
Weigh 1 g of 5-methylisoxazole-3-carboxylic acid; dissolve it in 10 mL of chloroform in a reactor. Place the reactor in an ice bath and add 1.2 mL of thionyl chloride. Gradually add 1 mL of triethylamine. Reduce the volume under vacuum after the reaction is complete. Add dichloromethane (10 mL) and then add the desired substituted aniline (see the table above) and mix thoroughly with cooling from an ice bath. Add triethylamine (1 mL), let it react for about 30 minutes, and monitor the reaction by thin layer chromatography. Wait till the reaction is complete and concentrate under vacuum. Use a separatory funnel to separate the organic and aqueous layers. Keep the organic layer; add anhydrous magnesium sulfate; let it sit for about 30 minutes; filter off magnesium sulfate and keep the filtered organic liquid; dry the organic liquid to obtain the crude product; re-crystallize in absolute alcohol to obtain product 5a and 5b. 
Method 2:
Weigh 5-methylisoxazole-3-carboxylic acid (2 g), N-hydroxysuccinimide (2 g) and coupling agent N,Nxe2x80x2-dicyclohexylcarbodiimide (3.6 g); add the desired substituted aniline, and crystallize in absolute alcohol to make 5axcx9c5k.
Results of the syntheses and characteristics of the leflunomide analogs are shown as follows:
[Compound 5a] N-(Phenyl)-3-carboxamidyl-5-methylisoxazole 
mp: 109xcx9c110xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=270 (4.025); IR (KBr): xcexdcmxe2x88x921=3339 (Nxe2x80x94H), 1677(Cxe2x95x90O), 1598 (Cxe2x95x90C); MS (EI, 70ev): 202 (M+, 100), 119 (65); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.47 (3H, s, CH3), 6.65 (1H, s, CCH), 7.11 (1H, t, J=6.6 Hz, H4-phenyl), 7.34 (2H, t, J=7.5 Hz, H3,5-phenyl), 7.80 (2H, d, J=9 Hz, H2,6-phenyl), 10.64 (1H, s, NH); 13C-NMR (DMSO-d6, 75 MHz): xcex4(ppm); 12.1, 101.9, 120.9, 124.6, 129.0, 138.4, 157.8, 159.6, 171.7; CHN Analysis (Theory/Experiment) based on C11H10N2O2; % C; (65.34/65.28), % H; (4.98/4.95), % N; (13.85/13.72).
[Compound 5b] N-(2-Chlorophenyl)-3-carboxamidyl-5-methylisoxazole) 
mp: 90xcx9c92xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=250 (3.33); IR (KBr): xcexdcmxe2x88x921=3326 (Nxe2x80x94H), 1626 (Cxe2x95x90O), 1575 (Cxe2x95x90C); MS (EI, 70ev): 236 (M+), 201 (100), 173 (60); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.50 (3H, s, CH3), 6.69 (1H, s, CCH), 7.29 (1H, t, J=7.7 Hz, H4-phenyl), 7.39 (1H, t, J=7.7 Hz, H5-phenyl), 7.55 (1H, d, J=7.8 Hz, H3-phenyl), 7.71 (1H, d, J=7.9 Hz, H6-phenyl), 10.19 (1H, s, NH); 13C-NMR (DMSO-d6, 75 MHz): xcex4(ppm); 12.24, 101.8, 127.1, 128.0, 129.9, 134.2, 157.7, 158.9, 172.2; CHN Analysis (Theory/Experiment) based on C11H9ClN2O2. % C; (55.83/55.36), % H; (3.83/3.77), % N; (11.84/11.99).
[Compound 5c] N-(3-Chlorophenyl)-3-carboxamidyl-5-methylisoxazole 
mp: 91xcx9c93xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=260 (4.01); IR (KBr): xcexdcmxe2x88x921=3347 (Nxe2x80x94H), 1689 (Cxe2x95x90O), 1593 (Cxe2x95x90C); MS (EI, 70ev): 236 (M+), 173 (100), 153 (80); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.49 (3H, s, CH3), 6.66 (1H, s, CCH), 7.18 (1H, d, J=8 Hz, H4-phenyl), 7.37 (1H, t, J=8.1 Hz, H5-phenyl), 7.72 (1H, d, J=8.3 Hz, H6-phenyl), 7.94 (1H, s, H2-phenyl), 10.82 (1H, s, NH); 13C-NMR (DMSO-6, 75 MHz): xcex4(ppm); 12.2, 120.0, 119.2, 120.3, 124.3, 130.7,133.3, 139.9,.158.0, 159.3, 171.9; CHN Analysis (Theory/Experiment) based on C11H9ClN2O2; % C; (55.83/55.93), % H; (3.83/3.75), % N; (11.84/11.84).
[Compound 5d] N-(4-Chlorophenyl)-3carboxamidyl-5-methyisoxazole 
mp: 135xcx9c140xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=234 (4.55), 269 (4.74); IR (KBr): xcexdcmxe2x88x921=3329 (Nxe2x80x94H), 1683 (Cxe2x95x90O), 1528 (Cxe2x95x90C); MS (EI, 70ev): 236 (100), 201(M+); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.50 (3H, S, CH3), 6.68 (1H, s, CCH), 7.71 (2H, d, J=8.1 Hz, H3,5-phenyl), 8.02 (2H, d, J=7.8 Hz, H2,6-phenyl), 10.98 (1H, s, NH); 13C-NMR (DMSO-6, 75 MHz): xcex4(ppm); 12.1, 101.9, 122.4, 128.4, 128.9, 137.4, 157.9, 159.4, 171.7; CHN Analysis (Theory/Experiment) based on C11H9ClN2O2; % C; (55.83/55.93), % H; (3.83/3.98), % N; (11.84/11.17)
[Compound 5e] N-(3-Trifluoromethyl)-3-carboxamidyl-5-methylisoxazole 
mp: 156xcx9c158xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=255 (4.098); IR (KBr): 3330 (Nxe2x80x94H), 1683 (Cxe2x95x90O), 1557 (Cxe2x95x90C); MS (EI, 70ev): 271 (M+, 90), 102 (100); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.49 (3H, s, CH3), 6.68 (1H, s, CCH), 7.47 (1H, d, J=7.3 Hz, H4-phenyl), 7.57 (1H, t, J=7.9 Hz, H5-phenyl), 8.04 (1H, d, J=8.1 Hz, H6-phenyl), 8.26 (1H, s, H2-phenyl), 10.99 (1H, s,NH); 13C-NMR (DMSO-d6, 75 MHz): xcex4(ppm); 12.2, 101.9, 117.0, 117.1, 120.9, 124.5, 130.1, 130.3, 139.3, 158.2, 159.3, 171.9; CHN Analysis (Theory/Experiment) based on C12H9F3N2O2; % C; (53.34/53.39), % H; (3.36/3.59), % N; (10.37/10.71).
[Compound 5f] N-(4-Trifluoromethylphenyl)3-carboxamidyl-5-methylisoxazole 
mp 179xcx9c180xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=268 (3.887); IR (KBr): xcexdcmxe2x88x921=3334 (Nxe2x80x94H), 1677(Cxe2x95x90O), 1539 (Cxe2x95x90C); MS (EI, 70ev): 270 (M+, 100); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.49 (3H, s, CH3), 6.68 (1H, s, CCH), 7.71 (2H, d, J=8 Hz, H2,6-phenyl), 8.03 (2H, d, J=8.2 Hz, H3,5-phenyl), 10.99 (1H, s, NH); 13C-NMR (DMSO-d6, 75 MHz): xcex4(ppm); 12.1, 101.9, 122.4, 128.4, 128.9, 137.4, 157.8, 159.4, 171.7; CHN Analysis (Theory/Experiment) based on C12H9F3N2O2; % C; (53.34/53.01), % H; (3.36/3.46), % N; (10.37/10.38).
[Compound 5g] N-(2,4-Dichlorophenyl)-3carboxamidyl-5-methylisoxazole 
mp: 148xcx9c156xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=250 (4.89), 277 (3.88); IR (KBr): xcexdcmxe2x88x921=3348 (Nxe2x80x94H), 1697 (Cxe2x95x90O), 1589 (Cxe2x95x90C) MS (EI, 70ev): 271 (100), 154(M+); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.50 (3H, s, CH3), 6.67 (1H, s, CCH), 7.41 (1H, d, J=8.7 Hz H5-phenyl), 7.66 (1H, d, J=2.2 Hz, H3-phenyl, 7.83 (1H, d, J=8.7 Hz, H6-phenyl), 10.25 (1H, s, NH); CHN Analysis (Theory/Experiment) based on C11H8Cl2N2O2; % C; (48.73/48.14), % H; (2.97/2.97), % N; (10.33/10.35).
[Compound 5h] N-(4-Methoxyphenyl)-3carboxamidyl-5-methylisoxazole 
mp: 124xcx9c126xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=227 (3.76), 288 (3.69); IR (KBr): xcexdcmxe2x88x921=3332 (Nxe2x80x94H), 1672 (Cxe2x95x90O), 1521 (Cxe2x95x90C); MS (EI, 70ev): 232 (M+, 100), 149 (64); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.48 (3H, s, CH3), 3.73 (3H, s, OCH3), 6.63 (1H, s, CH3), 6.91 (2H, d, J=8 Hz, H3,5-phenyl), 7.69 (2H, d, J=8.1 Hz, H2,6-phenyl), 10.52 (1H, s, NH); 13C-NMR (DMSO-d6, 75 MHz): xcex4(ppm); 10 12.2, 55.5, 101.9, 114.1, 122.3, 122.4, 131.5, 156.3, 157.4, 159.7, 171.6; CHN Analysis (Theory/Experiment) based on C11H12N2O3; % C; (62.06/62.12), % H; (5.21/5.23), % N; (12.06/12.33);
[Compound 5i] N-(3,4,5-Trimethoxyphenyl)-3-carboxamidyl-5-methylisoxazole 
mp: 170xcx9c172xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=293 (3.439); IR (KBr): xcexdcmxe2x88x921=3326 (Nxe2x80x94H), 1688 (Cxe2x95x90O), 1557 (Cxe2x95x90C); MS (EI, 70ev): 292 (M+, 100), 277 (20); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.49 (3H, s, CH3), 3.63 (6H, s, 2OCH3), 3.75 (3H, s, OCH3), 6.35 (1H, s, CCH3), 7.25 (2H, s, H2,6-phenyl), 10.52 (1H, s, NH); CHN Analysis (Theory/Experiment) based on C11H12N2O3; % C; (57.53/57.65), % H; (5.52/5.61), % N; (9.58/9.59).
[Compound 5j] 4-[(5-Methylisoxazole-3-carbonyl)-amino]-benzoic acid 
mp: 267xcx9c270xc2x0 C.; UV (MeOH ): mxcexmaxnm (log xcex5)=284 (4.27); IR (KBr): xcexdcmxe2x88x921=3342 (Nxe2x80x94H), 1685 (Cxe2x95x90O), 1529 (Cxe2x95x90C); MS (FAB): m/z 247 (MH+); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.50 (3H, s, CH3), 6.69 (1H, s, CCH), 7.94 (4H, s, H2,3,5,6-phenyl), 10.94 (1H, s, NH); 13C-NMR (DMSO-d6, 75 MHz): xcex4(ppm); 12.2, 102.1, 120.2, 126.6, 130.6, 142.5, 158.2, 159.4, 167.2, 171.9; CHN Analysis (Theory/Experiment) based on C11H9ClN2O2; % C; (58.54/58.46), % H; (4.09/4.10), % N; (11.38/11.42).
[Compound 5k] N-(4-Fluorophenyl)-3-carboxamidyl-5-methylisoxazole 
mp: 136xcx9c138xc2x0 C.; UV (MeOH): xcexmaxnm (log xcex5)=271 (4.19); IR (KBr): xcexdcmxe2x88x921=3342 (Nxe2x80x94H), 1685 (Cxe2x95x90O), 1529 (Cxe2x95x90C); MS (EI, 70ev): 220 (M+, 100), 137 (30), 110 (38); 1H-NMR (DMSO-d6, xe2x88x92300 MHz): xcex4(ppm); 2.49 (3H, s, CH3), 6.65 (1H, s, CCH), 7.10 (2H, dd, J=5.2, 5.1 Hz, H2,6-phenyl), 7.80 (2H, dd, J=8.8, 8.6 Hz, H3,5-phenyl), 10.71 (1H, s, NH); 13C-NMR (DMSO-d6, 75 MHz): xcex4(ppm); 12.2, 101.9, 115.5, 122.7, 134.7, 157.7, 159.5, 160.6, 171.7; CHN Analysis (Theory/Experiment) based on C12H9FN2O2; % C; (60.0/60.17), % H; (4.12/4.17), % N; (12.72/12.47).
C-1. Animal Used
Wistar Albino Rats of 4 to 6 weeks old with weights of 100-150 g were used for the studies.
C-2. Preparation of reagents
1.1 % carrageenan solution
Weigh 30 mg of xcex-carrageenan (Sigma Chemical) powder; add 3 mL of saline to make the 1% carrageenan solution.
2. CMC (carboxymethyl cellulose) solution
Weigh 30 mg of xcex-carrageenan (Sigma Chemical) powder; add 3 mL of saline to make the 1% carrageenan solution.
3. Dexamethasone suspension
Weigh 7.5 mg of dexamethone (Sigma Chemical Co., USA), add 5 mL of 1% CMC solution, shake to make the 1.5 mg/mL dexamethasone suspension.
4. Ibuprofen suspension Weigh 10 mg of ibuprofen (Sigma Chemical Co., USA), add 10 mL of 1% CMC solution, shake to make the 1 mg/ml ibuprofen suspension.
5. Suspensions of testing compounds
Individually weigh 10 mg of each testing compound; add 10 mL of 1% CMC and shake to make the suspension.
6. Solution used to measure the inflammation
Weigh 0.4-0.5 g of NaCl; add 5 mL of surfactant, Lubricant IMBIBNTE BBC97 (Chimifoto ornano S. P. A. Italy); Add de-ionized water to make 1 liter.
C-3. Efficacy and Results
In the present invention, Carrageenan was used to stimulate the inflammation on the rear left footpad of the rat. The inflammation on the left footpad of each rat was measured for rats with and without treatment. Treatment includes leflunomide analogs, dexamethasone, ibuprofen, and Malononitrilamide (MNA). Measurements of the inflamation at pre-determined time points were made.
The rats were weighed and divided into three groups: (1) Control Group, (2) Test Group, and (3) Comparison Group. For each compound, 5 rats were used and marked on the tails. Before injecting carrageenan, the volume of each left footpad was measured (V0). Each rat was injected in the back as follows:
(1) Control Group: 1% CMC for Control Group,
(2) Testing Group: testing compound (10 mg/kg each) in 1% CMC, and
(3) Comparison Group: dexamethasone (1.5 mg/kg in 1% CMC), ibuprofen 10 mg/kg in 1% CMC, MNA in 1% CMC.
One hour later, 0.05 mL of 1% carrageenan was injected onto the rear footpad of each rat to initiate the inflammation. Measure the volume of the rear left footpad (Vt) at 0.5, 1, 2, 3, 4, and 5 hours.
The Edema Rate (E%) and the Inhibition Rate (I%) are calculated as follows and the results of the in-vivo studies are summarized in Table 1 and Table 2.             E      ⁢              xe2x80x83            ⁢      %        =                                        V            t                    -                      V            0                                    V          0                    xc3x97      100      ⁢      %                  I      ⁢              xe2x80x83            ⁢      %        =                                        E            c                    -                      E            t                                    E          c                    xc3x97      100      ⁢      %      
V0=Volume (mL) of the rear left footpad before the injection of Carrageenan.
Vt=Volume (mL) of the rear left footpad at xe2x80x9ctxe2x80x9d time after the injection of Carrageenan
Ec=Edema Rate of the, Control Group
Et=Edema Rate of the Testing Group and Comparison Group
In the present invention, a compound with the following general formula (I) is disclosed, 
wherein R is xe2x80x94H, 2-Cl, 3-Cl, 4-Cl, 2,4-(Cl)2, 2-F, 3-F, 4-F, 2,4-(F)2, 2-Br, 3-Br, 4-Br, 2,4-(Br)2, 2-CF3, 3-CF3, 4-CF3, 2,4-(CF3)2, 2-COOH, 3-COOH, 4-COOH, 2,4-(COOH)2, 2-OCH3, 3-OCH3, 4-OCH3, 3,4,5-(OCH3)3, 2-NHxe2x80x94COxe2x80x94CH2Cl, 4-NHxe2x80x94COxe2x80x94CH2Cl, 2-NHxe2x80x94COxe2x80x94CH2Br, or 4-NHxe2x80x94COxe2x80x94CH2Br.
Also disclosed is a physiological tolerable salt of the compound of the formula (I).
The present invention also relates to a pharmaceutical composition comprising an effective amount of at least one compound of the formula (I) and/or a physiologically tolerable salt of the compound of the formula (I), in addition to pharmaceutically suitable excipients, additives, and/or active compounds and auxiliaries.
Examples of suitable forms of the pharmaceutical composition are tablets, coated tablets, injectable solutions, suspensions, emulsions, powders, granules, (micro)capsules, suppositories, and syrups.
Also disclosed in the present invention is a method comprising treating rheumatoid arthritis by administering to a patient an effective amount of the pharmaceutical composition described above.
Also disclosed is a method of treating rheumatoid arthritis comprising administering to a patient the pharmaceutical composition and one of the drugs on the market already used to treat rheumatoid arthritis comprising dexamethasone, ibuprofen, leflunomide, malononitrilamide, diclofenac sodium, diclofenac potassium, naproxen, or naproxen sodium.